Income Taxes - Schedule of Company's Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Deferred revenue	$ 6,073	$ 15,491
Net operating loss carry forward	80,620	72,232
Stock-based compensation	21,257	12,721
Research and development credits	22,616	13,897
Depreciation, amortization and other		109
Accruals and reserves	10,544	6,530
Total deferred tax assets	141,110	120,980
Less: valuation allowance	(120,807)	(98,671)
Total net deferred tax assets	20,303	22,309
Depreciation, amortization, and other	(2,674)
Convertible Notes	(17,629)	(22,309)
Total deferred tax liabilities	(20,303)	(22,309)
Net deferred tax assets
Net current deferred tax assets (included in "Prepaid expenses and other current assets")	5,541	3,800
Net non-current deferred tax assets
Net current deferred tax liabilities
Net non-current deferred tax liabilities (included in "Other non-current liabilities")	(5,541)	(3,800)
Net deferred tax assets